The present invention relates to asphalt compositions containing polymers for modification of the properties of the asphalt. More particularly, this invention relates to such compositions containing new polymers which impart lower processing viscosity to the asphalt while maintaining the desired high softening point for the composition.
Asphalt is a common material utilized for the preparation of paving and roofing materials and also for coatings such as pipe coatings and tank liners. While the material is suitable in many respects, it inherently is deficient in some physical properties which it would be highly desirable to improve. Efforts have been made in this direction by addition of certain conjugated diene rubbers, ethylene containing plastics like EVA and polyethylene, neoprene, resins, fillers and other materials for the modification of one or more of the physical properties of the asphalt. Each of these added materials modifies the asphalt in one respect or another but certain deficiencies can be noted in all modifiers proposed. For example, some of them have excellent weather resistance, sealing and bonding properties but are often deficient with respect to warm tack, modulus, hardness and other physical properties; and some of them improve only the high temperature performance of asphalt, some only improve the low temperature performance of asphalt, while some lack thermal stability or mixing stability with asphalt.
Since the late 1960s, diene polymer rubbers such as styrene-butadiene rubber and styrene-rubber block copolymers such as styrene-butadiene-styrene and styrene-isoprenestyrene block copolymers have been used to dramatically improve the thermal and mechanical properties of asphalts. Practical application of the rubber addition approach requires that the blended product retain improved properties and homogeneity during transportation, storage and processing. Long term performance of elastomer-modified asphalts also depends on the ability of the blend to maintain thermal and chemical stability.
Such polymers have been found to be very advantageous but in some end uses, such as roll roofing membranes, high processing viscosity of blends of asphalt and such polymers leads to reduced manufacturing rates. Other attempts at lowering the processing viscosity, such as reducing molecular weight or polymer content or adding oil, have proved to be undesirable because the softening point of the composition was lowered to such an extent that adequate slump resistance could not be achieved. Also, the processing stability of blends of some of the commercially used polymers could advantageously be improved to provide a wider processing window. Therefore, it can be seen that it would be highly advantageous to have a asphalt blend which is characterized in that the ring and ball softening point is relatively high, at least 118.degree. C. to 125.degree. C., the processing viscosity is lower than currently possible with the popular commercially available materials, i.e., preferably less than 3000 centipoise, and the processing stability of the blend is improved such that higher processing temperatures may be used.